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The Juno Mission

Juno was launched on 5 August 2011 from Cape Canaveral in Florida and went into orbit around Jupiter on 4 July 2016 after a journey covering almost 3 billion kilometres.Juno is scheduled to orbit Jupiter for about five years . While orbiting some distance from the planet, Juno will be sent closer to the planet’s surface for shorter periods. In this way, the extreme particle radiation in the planet’s magnetic field will not destroy the instruments on board the spacecraft. Juno travels at a speed of approx. 96,000 km/hour in relation to Earth.

The main goal of the mission is to study how Jupiter was formed as well as its development by:

Mapping out its magnetic and gravitational fields to identify its internal structure.

Examining the magnetosphere around its poles to find out more about how the planet’s enormous magnetic fields affect its atmosphere.

Looking at how much water its atmosphere contains, which may provide new knowledge about how the planets were formed.

According to new research from the Juno mission published in Nature with participation from DTU Space, the dynamo forming the magnetic field around Jupiter is much stronger and more uneven than what has been observed on the other planets of the solar system.

The largest planet in the solar system, Jupiter, continues to surprise researchers. Last year they concluded that its magnetic field is significantly different than previously assumed. And now it turns out that the dynamo, which is the driving force behind the magnetic field, does not look like anything seen on the other planets of the solar system. The dynamo at the planet core is both stronger and more uneven in strength and distribution.

The findings are based on readings from NASA’s unmanned Juno spacecraft, which has been orbiting the gas giant since 2016 with equipment from DTU Space on board for mapping the planet in unprecedented detail. The new findings have just been published in the scientific journal Nature.

“The images currently coming in paint a completely different picture of Jupiter than we expected. It is both very exciting and quite surprising. The dynamo generating the magnetic field looks like nothing we know from other planets previously investigated, including Earth. The system is actually more similar to the one generating the Sun’s magnetic field,” says Professor John Leif Jørgensen, Head of Section, DTU Space, who is responsible for DTU’s part in the mission.

He and his DTU colleague, Professor José Merayo, are co-authors of the new Nature article, which has researchers from Harvard University and NASA as its main authors.

It also appears that while Jupiter has an nearly normal magnetic field on the southern hemisphere, it also has an extra and much more powerful south pole at the equator, i.e. on the side of the planet. The north pole, on the other hand, is almost completely missing and is distributed in a band across the planet’s northern hemisphere.

Conductive materials cause variations in the dynamo
Researchers believe that the powerful and unevenly distributed dynamo may be due to the fact that the dynamo is covered by an thin liquid layer of highly conductive materials, and that sudden changes in the conductivity of the layer probably occur. The dynamo itself is located deep within Jupiter—0.5-0.7RJ down in Jupiter radii, 71,492km, i.e. 11 times greater than Earth’s—and gets its energy from the convection of this depth.

Researchers believe the field from this deep dynamo is dipole-like as on Earth, i.e. a field similar to the one you get from a bar magnet. However, the thin liquid layers redistributes this field dramatically, resulting in the magnetic field around Jupiter, which is measured by the Juno mission.

“The mechanism of the dynamo is surprising. All other planets examined have essentially the same dynamo as Earth,” says John Leif Jørgensen.

Each trip around Jupiter reveals new phenomena
Juno’s trajectory was designed specifically to uncover the secrets of the magnetic field on Jupiter.

This is achieved by setting the spacecraft on a very elliptical trajectory, where it gets close to the planet surface at its closest and far away form the ionizing radiation belts of the planet at its farthest. In this way, data is obtained near the planet and the equipment used on Juno is not destroyed by the radiation in the area.

"The images currently coming in paint a completely different picture of Jupiter than we expected. It is both very exciting and quite surprising."

Professor John Leif Jørgensen

The first parts of Jupiter alone revealed a magnetic field twice as powerful as previously assumed. The new discoveries described in Nature are based on Juno’s first eight orbits around Jupiter. Each trip takes 53 days, and this week, the 15th orbit comes to a close.

“After each new orbit, the magnetic field reveals even more surprising phenomena,” says John Leif Jørgensen.

“As we receive more data from each orbit, the image that Juno’s trajectory reveals of Jupiter becomes increasingly clear. So there will definitely be more exciting results from the mission in the future.”

Generally, a better insight into the structure of the dynamo on Jupiter can be of great significance to our understanding of how the Sun’s magnetic field works. Jupiter is close to being made like a sun.

“However, Jupiter is a bit too small to burn as bright as the Sun,” says John Leif Jørgensen.

“We can get close to Jupiter’s clouds. But due to the Sun’s heat, we cannot get close enough to its surface to get detailed readings, which makes its magnetic field very difficult to study in greater detail. Nevertheless, it is very important to understand it, because it is the Sun’s magnetic field that creates the space weather which is so important for the climate here on Earth”.

Top illustration: The yellow/red area is the north pole, which stretches like a band across the northern hemisphere. Middle right: The blue/green area is Jupiter’s “extra” south pole. Below, you can see a small green area, which is the “normal” south pole. (Illustration: Nature/NASA/DTU Space).

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With space as the starting point we do scientific research, develop technology, advice authorities, educate scientists and engineers for the benefit of society. This includes exploring our solar system, the universe, the Earth's magnetic field and monitoring Earth's climate and environment from space.